1. Field of the Invention
At least one example in accordance with the present invention relates generally to providing low voltage DC power to a controller from AC mains.
2. Discussion of Related Art
With the advent of modern microelectronics, the DC voltage levels necessary to power microelectronic circuits has been dropping, to the point where the latest microprocessors can run from a supply as low as 0.8 Vdc. However, typical embedded microcontrollers used in many industrial products run from DC supplies ranging from 1.8 to 3.3 Vdc. The current levels required for these devices may range from 145 A (for the latest, most powerful quad-core processor) to microamperes (for the latest, low-power controllers). These low power controllers are oftentimes utilized in the distributed sensors and actuators of emerging applications such as “Smart Outlets” or a “Smart Grid”.
In the home automation and energy efficiency market, the demand for “Smart Outlets”, “Smart Grids” and other intelligent power products that are more cost and energy efficient is quickly growing. For example, such “Smart Outlets” may prevent the flow of energy to an outlet when it detects that a device coupled to the outlet has gone into standby mode. Additionally, a plurality of “Smart Outlets” may also be networked together to more efficiently monitor and control the distribution of power to the plurality of outlets. On a larger scale, a “Smart Grid” is an electrical grid that gathers, distributes and acts on information regarding the behavior of suppliers and consumers coupled to the grid to improve the efficiency of the electrical grid. As mentioned above, microelectronic devices (e.g., sensors, actuators, controllers, processors etc.) within “Smart Outlets” or “Smart Grids” often utilize low-power controllers.
When low-power controllers receive power from the AC mains, there are two commonly used methods to provide the necessary low-power from AC mains: 1) a small Switch Mode Power Supply (SMPS) and 2) a capacitor (cap) dropper circuit. A cap dropper circuit is often used when a low current (e.g., <30 mA average) DC supply that is not galvanically isolated from the AC mains is sufficient. A cap dropper circuit typically utilizes a series capacitive voltage divider to provide the desired low power.